MRG: tell dependabot to ignore upgrades to byteorder, chrono, `on…

…ce_cell`, and `wasm-bindgen` (#3065)

This uses dependabot `ignore` per
[docs](https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuring-dependabot-version-updates)
to pin the packages needed for `sourmash_plugin_branchwater
compatibility per #2944`.

Motivation:
* embarrassment from #3060
and then #3064

Related issues:
* Fixes #2944

.github/dependabot.yml

@@ -12,6 +12,11 @@ updates:
   allow:
     - dependency-type: "direct"
   open-pull-requests-limit: 10
+  ignore:
+    - dependency-name: "byteorder"
+    - dependency-name: "wasm-bindgen"
+    - dependency-name: "once_cell"
+    - dependency-name: "chrono"
 - package-ecosystem: "github-actions"
   directory: "/"
   schedule: